The present invention is directed to stepping motors, and in particular, to an improved 2-step bi-directional stepping motor that is can reliably run in either direction merely dependent upon a specific pulse-current scheme used therewith. The present invention, among other applications, is particularly suited for use in connection with electronic quartz wristwatches or other micro-mechanical devices.
xe2x80x9cMulti-Stepxe2x80x9d stepping motors, having multiple stator and/or rotor poles, or those of the so-called xe2x80x9cLavetxe2x80x9d type, are well known in the art. For example, while the xe2x80x9cmultiple-stepxe2x80x9d motors run in both directions depending on the direction of the xe2x80x9crotor-drivingxe2x80x9d electromagnetic field, the xe2x80x9cLavetxe2x80x9d type motor may have one preferred rotational direction achievable through the rotor""s xe2x80x9crest position.xe2x80x9d The prior art provides a plurality of examples illustrating the foregoing constructions.
Alternating rectangular pulse-current schemes to drive rotors in 180 degree steps are also known. For example, in one such known configuration, an alternating rectangular current-pulse is applied to the motor coil, and the rotor magnet follows the changed magnetic flux in the stator, being pushed from its rest position to its opposite stable rest position, 180 degrees rotated. To continue the rotation of the rotor, the current-pulse is reversed and the rotor is pushed in the same rotational direction back to its starting-position, thus completing one revolution in two steps. FIG. 6 exemplifies the relevant portion of a prior art stepping motor that is operable in the foregoing manner. As can be readily seen, typical of such a stepping motor is the specific positioning of the xe2x80x9crest position,xe2x80x9d which may be chosen as a function of the magnetic vector of the electromagnetic flux generated by the motor coil. Geometries of the rotor or stator cutouts and/or the use of small permanent magnets can also play a significant part in the operation of such a stepping motor.
The foregoing exemplary stepping motor is widely used in electronic timepieces, notwithstanding its perceived deficiency in being unable to run in both a clockwise and counter-clockwise direction. Being able to run in both directions would be significantly advantageous, for example, so as to be able to perform a quick xe2x80x9ctime-settingxe2x80x9d function in radio controlled watches.
Bipolar current-pulse sequences have been developed to make the foregoing type of stepping motor run in a reverse direction. For example, the rotor may be accelerated for a short distance (i.e. 45 degrees) from its rest position in the reverse direction by a first initial pulse so that when it passes its stator flux axis, a reversed pulse pushes it to the opposite stable position. Thereafter, it may again drop 45 degrees backwards, against the rotational direction, into its opposite stable Rest Position when the coil current is off. Unfortunately however, this particular stepping motor design provides for rough running, and additionally, due to the additionally required pulse per step, leads to higher power consumption while running in reverse. Furthermore, if the reverse pulse is not accurately applied in intensity and time, the rotor may undesirably pass its alternating rest positions thus leading to an undesirable xe2x80x9cone step per revolutionxe2x80x9d result.
It can thus be seen that it is difficult to ensure a reliable 2-Step reverse run in known xe2x80x9cLavetxe2x80x9d type stepping motors. However, the prior art is not without its attempts to do so.
For example, U.S. Pat. No. 4,361,790 attempts to overcome the foregoing deficiencies by the implementation of alternating the current direction within two respective coils. In particular, the two coils always operate simultaneously by a certain current-pulse scheme, which alleges, among other things, the elimination of the need to double the coil volume. U.S. Pat. No. 4,361,790 proposes a current-pulse scheme in which four steps per revolution, each of which is 90 degrees, are made. Such is the case in both the clockwise and counter-clockwise direction.
However, the present inventors still believe further improvements over the state of the art are necessary, both to overcome the foregoing explicitly perceived deficiencies as well as to overcome deficiencies that would be apparent to those skilled in the art. For example, one desirous feature is to construct a smooth running xe2x80x9cLavetxe2x80x9d type stepping motor that can make two steps per revolution, in both the clockwise or counter-clockwise direction. Secondly, it is desirous to provide such a stepping motor that does not have a preferred rotational direction. In particular, it is desired that the shape of the current-pulses, applied to the motor coils, determine the direction of rotation of the rotor. The present invention achieves the foregoing and below mentioned objectives, as well as overcomes the perceived deficiencies in the prior art.
It is therefore an object of the present invention to provide an improved stepping motor that overcomes the foregoing perceived deficiencies.
It is another object of the present invention to provide an improved stepping motor that more smoothly runs in both the forward and reverse direction.
It is yet another object of the present invention to provide an improved stepping motor that does not increase the power consumption from that seen in prior art bi-directional stepping motors, namely, it is an object of the present invention to provide an improved current-pulse scheme that has the same power consumption regardless of the rotational direction of the rotor.
It is yet another object of the present invention to provide an improved stepping motor that merely needs to rely on the pulse-current scheme for its directional rotation.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combination of elements and arrangement of parts and sequence of steps which will be exemplified in the construction, illustration and description hereinafter set forth, and the scope of the invention will be indicated in the claims.
Generally speaking, in accordance with the present invention, a stepping motor in which a rotor is rotatable in steps of 180 degrees each, is provided. In one embodiment, the stepping motor comprises a rotor comprising a permanent magnet and rotatably mounted about an axis and providing a permanent magnetic field; a first electrical coil and a second electrical coil; a stator comprising three pole faces arranged around the rotor and arms on which the electrical coils are mounted; and a control circuit, coupled to the first and second electrical coils, for applying electrical pulses independently to each coil and for controlling the polarity thereof, the coils producing magnetic fields in response to the pulses and wherein the rotor is rotatable in response to the magnetic fields; wherein each step of 180 degrees is effectuated by providing to the first coil, a first pulse of a first polarity and a second pulse of a second polarity; and to said second coil, a pulse of the second polarity simultaneously with the providing of the second pulse to the first coil; wherein during the providing of the first pulse to the first coil, there is no pulse being provided to the second coil.
Furthermore, the rotation of the second 180 degree step is preferably achieved by providing to the first coil, a third pulse of the second polarity and a fourth pulse of the first polarity; and to said second coil, a pulse of the first polarity simultaneously with the providing of the fourth pulse to the first coil; wherein during the providing the third pulse to the first coil, there is no pulse being provided to the second coil.
In a particular arrangement, each step of 180 degrees is effectuated by a rotation of the rotor a first X degrees and then by a further rotation of the rotor the remaining 180-X degrees, wherein X is a predetermined number greater than zero. In a specific configuration, the value of X is approximately 30 degrees and the three pole faces are arranged at an angular spacing of approximately 120 degrees with respect to each other. In this manner, the rotation of the rotor the approximately X degrees is achieved by providing to the first coil, a first pulse of a first polarity; and wherein the rotation of the rotor the approximately 180-X degrees to complete a step is achieved by providing to the first coil a second pulse of a second polarity simultaneously with the providing of a pulse of the second polarity to the second coil. The second step of 180 degrees is effectuated by the additional rotation of the rotor X degrees and then by a further rotation of the rotor the remaining 180-X degrees; wherein the additional rotation of the rotor X degrees is achieved by providing to the first coil, a third pulse of the second polarity; and wherein the rotation of the rotor the approximately 180-X degrees to complete the second step is achieved by providing to the first coil a fourth pulse of the first polarity simultaneously with the providing of a pulse of the first polarity to the second coil; whereby during the providing of the third pulse to the first coil, there is no pulse being provided to the second coil.
In a preferred embodiment, the stepping motor constructed in accordance with the present invention is incorporated into a timepiece, such as a wristwatch.